BC12-D A65 to A75 Conversion

[barnstmr]

Re: BC12-D A65 to A75 Conversion

the 28 on left mag ( lower) and 30 on right was done with no impulse mags to let the engine start easier with the left firing first. In fact if she kicked back then you went to left mag only for starting.

Forrest, Technically, you want to retard timing for improved starting. So you need to start on the mag which fires later. I understood what you meant, but some might get confused on this.

[Larry Lyons]

Re: BC12-D A65 to A75 Conversion

When I was I kid I watched dad tune his 1/4 midget that way. Memories I had forgotten, thanks Forrest. Larry

[Forrest Barber]

Re: BC12-D A65 to A75 Conversion

Then we have another reason: the 28 on left mag ( lower) and 30 on right was done with no impulse mags to let the engine start easier with the left firing first. In fact if she kicked back then you went to left mag only for starting. I timed my first set of Case mags on an A-65 in 1950 at age 8.... I can discuss flame front and all those other comments with the best of them, the slow turning little engines (and there are many of them ) will run okay if they are close on timing
Any body ever flame tune a Model A Ford aircraft engine at night just watching the flame coming out of the short stacks?

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

On the timing issue, early A65's had both mags set to one degree setting. The mags fired one set of lower plugs and one set of upper plugs. If you changed wiring and had a single mag firing all upper or all lower plugs, then the timing split.

I have seen one case( a C series) that had the cylinder holes bored to A65 size, it had no Data plate and I was told it was an A65-12 from a M18 Mite.

I had a Cessna 140 with a C85-14.

I still can't find information that an A65-14 was ever produced or installed into any airframe. If nothing exists my congratulation for acquiring engineering approval for installation of an engine that doesn't exist.
EO

[NY86]

Re: BC12-D A65 to A75 Conversion

Staggered timing fires the lower plugs first. The reason is because the lower plugs are closer to the exhaust valves and the mixture there is weaker. A weaker mixture burns slower, so you want to light it earlier.

[barnstmr]

Re: BC12-D A65 to A75 Conversion

The staggered timing provides for a more complete (more efficient) fuel burn, particularly effective at higher RPM. If you can imagine this... the longer burn pulls more energy from the fuel and actually eeks out a little more power for a given set of power conditions... manifold pressure/RPM/fuel flow rate. The trade off though is higher heat from combustion (more energy) but in trade for a greater demand for cooling. Since the A75 has better oil flow in the piston, etc as discussed, Continental specified the staggered timing on the A75. But the A65 (with lesser piston cooling) has a more conservative (cooler burning) timing specification. Hope that is clearer than mud.

[lfries]

Re: BC12-D A65 to A75 Conversion

In searching for a 337 that Forest said was used to make the A75 conversion I have been buying a lot of CD's on Taylorcrafts advertised with an A-75. Just got one recorded on the FAA CD but not signed off by a DER or the FAA. I assume it is worthless as supporting documentation?

[cvavon]

Re: BC12-D A65 to A75 Conversion

All that the change it timing does is keeps the fuel burn going longer by retarding the timing on one mag witch lights the fire twice witch jest makes sure the fuel in the cylinder burns more completely and keeps the power stroke going longer witch could increase the horse power some

[3Dreaming]

Re: BC12-D A65 to A75 Conversion

I know what the TCDS says, but still don't belive it. The only reason for staggered timing should be impulse on one mag

That doesn't make ant sense. The impulse makes no difference once the engine is running.

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

A65-14 is a legitimate animal. the Engine TCDS for A65 series says the following...

"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats
and guides."

This suggests it is similarly equipped as an A75. However one interesting difference with the A75 is that the magnetos on an A75 have staggered timing (29R/32L) and the A65-14 is the same as all other A65 series with both magnetos timed at 30 deg. If I owned this A65-14 and intended to operate it with a propeller that allows it to make the 2675 RPM, I think I might experiment with the staggered timing to see if the fuel consumption might improve.

I know what the TCDS says, but still don't belive it. The only reason for staggered timing should be impulse on one mag

[barnstmr]

Re: BC12-D A65 to A75 Conversion

A65-14 is a legitimate animal. the Engine TCDS for A65 series says the following...

"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats
and guides."

This suggests it is similarly equipped as an A75. However one interesting difference with the A75 is that the magnetos on an A75 have staggered timing (29R/32L) and the A65-14 is the same as all other A65 series with both magnetos timed at 30 deg. If I owned this A65-14 and intended to operate it with a propeller that allows it to make the 2675 RPM, I think I might experiment with the staggered timing to see if the fuel consumption might improve.

[NY86]

Re: BC12-D A65 to A75 Conversion

The -14 you reference above is a C90-14

Yeah, don't confuse the A series with the C series.

BTW, there is a spec for a C85-14 but I've never seen or heard of one.

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

According to recent article, The differences are: 8-no provision for starter...12- provision for starter, etc. 14-(the one your interested in) lord engine mount rather than traditional conical mount...16-vacuum pump adapter. They go on to say the best upgrade is to a 90 hp cont. but the 75 is a very good choice. TheA 75 at recommended cruise of 2350, produces 55.47 hp. The C75 produces 74.77 hp at 2275 The latter being a larger bore. They recommend the A75.( The 65 hp cont. delivers 55.42 hp @ 2150.) These figures are for engines in excellent condition. JC

The -14 you reference above is a C90-14 only which was for early Alon with vaccum system. I do not know of a a65-14 ever being built (not a conversion as discussed here) just like some people mistake there actually being an a65-12 which does not exist either

[jim cooper]

Re: BC12-D A65 to A75 Conversion

According to recent article, The differences are: 8-no provision for starter...12- provision for starter, etc. 14-(the one your interested in) lord engine mount rather than traditional conical mount...16-vacuum pump adapter. They go on to say the best upgrade is to a 90 hp cont. but the 75 is a very good choice. TheA 75 at recommended cruise of 2350, produces 55.47 hp. The C75 produces 74.77 hp at 2275 The latter being a larger bore. They recommend the A75.( The 65 hp cont. delivers 55.42 hp @ 2150.) These figures are for engines in excellent condition. JC

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

Boy, this A65-14 is an elusive creature. I haven't been able to find much information on it. The closest thing I could locate was a military O-170-7. This was considered to be the same as an A75-14. Perhaps the FAA made a typo in the TC document. It shows the O-170-7 as an A65-3 per note 4 but the O-170-7 was a down exhaust and the A65-3 was an up exhaust.
Does anybody have any added information on the A65-14. It doesn't look like TCM produced them with this designation.
EO